Stereoplotting method and apparatus

ABSTRACT

A method and apparatus for obtaining three-dimensional positional or coordinate information for a scene from two stereo images of that scene. An operator views a stereoscopic image of a scene which need not be in exact proportion to that scene, but can be distorted or warped. The operator traces along and records image positions of all conjugate points or lines of interest in the overlap area of the stereo images. Calculations convert these recorded image positions to the three-dimensional coordinates the actual points had in the image scene.

United States Patent [1 1 Forrest 1111 3,750,293 Aug. 7, 1973 STEREOPLOTTING METHOD .AND, APPARATUS lnventor: Robert B. Forrest, Union Lake,

Mich.

[731 Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: Mar. 10, 1971 [211 App]. No.: 122,844

[52] US. Cl 33/20 D [51] Int. Cl B431 13/16 [58] Field of Search 33/1 A,1 M, 20 D, 33/18 C; 353/5, 6, 7; 350/136 [56] References Cited I UNITEDSTATES PATENTS 3,088,209 5/1963 Schwidefsky 33/20 D 3,466,646 9/1969Lewin....- 33/1 M 2,303,099 11/1942 Wernstedt... 33/20 D 2,910,91011/1959 Rosenfeld 33/20 D FOREIGN PATENTS OR APPLICATIONS 686,324 5/1964Canada 33/20 D Primary Examiner-Harry N. Haroian AttorneyWilliam F.Thornton and Plante, Hartz, Smith & Thompson [57] ABSTRACT A method andapparatus for obtaining threedimensional positional or coordinateinformation for a scene from two stereo images of that scene. Anoperator views a stereoscopic image of a scene which need not be inexact proportion to that scene, but can be distorted or warped. Theoperator traces along and records image positions of all conjugatepoints or lines of interest in the overlap area of the stereo images.Calculations convert these recorded image positions to thethree-dimensional coordinates the actual points had in the image scene.

40 Claims, 5 Drawing Figures PATENTED M15 7 I975 3, 750.293

INVENTOR. 70/787225. fir/237 PATENIEMUE (I975 SHEEI 3 (IF 3STEREOPLOTTING METHOD AND APPARATUS BACKGROUND OF THE lNVENTlON 1. Fieldof the invention 1 Stereophotogrammetry the art of obtaining accuratethree-dimensional measurement of a scene from stereoscopic observationof two-dimensional images of that scene.

2. Description of the Prior Art Known stereoplotters include apparatusfor providing a three-dimensional model of a scene, apparatus forproviding a floating mark that can be moved from point to point in themodel to identify and select pointsof interest, and apparatus formeasuring the position of the floating mark to determine the modelcoordinate locations of the various selected points of interest. Theaccuracy of positional measurements of the selected points made withthese known stereoplotters depends upon the ability of the stereoplotterto provide an undistorted model of the scene. In one fundamentalstereoplotter the apparatus for providing a threedimensional model of ascene includes a a flat surface on which are placed two stereo images ofa scene taken from different vantage points. As used herein, the term"stereo images" is used to define any two twodimensional representationsof a three-dimensional scene taken from different vantage points, andincludes photographic records, hand drawings, machine drawings, and thelike. This fundamental stereoplotter also includes a binocular viewingdevice arranged so that an' operator will view one photograph with eacheye and thus see a three-dimensional image or model. A floating mark ismoved from point to point in the model, and the X, Y, and Z modelcoordinates of the floating mark at each point are measured directly.One advantage of this simple stereoplotter is that it is extremelysimple to construct and operate. The primary disadvantage is in thelimited accuracy of the X, Y, and Z coordinate measurements that can bemade for points in the scene. The three-dimensional model provided bythis fundamental stereoplotter normally will not be exact, scale modelof the photographed scene but will be a warped or distortedview of thatscene. To accurately reconstruct a true stereo model of the photographedscene, the stereophotographs must be positioned so that theirorientation with respect to each other corresponds to their orientationat the time of exposure. With this device, an operator can only adjustthe two photographs in the plane of the surface upon which they areplaced by changing their lateral separation and by rotating them. Sincethe photographs seldom are perfectly coplanar at the time of exposure,it is in general necessary to raise or tilt one of the photographs withrespect to the otherto create an unwarped stereo image. The fundamentalstereoplotter does not provide such adjustments. v

Other and more complicated stereoplotters overcome some of thedeficiencies of the simple device described above. These devices, calledprojection stereoplotters, enable a physical reconstruction of thecamera geometry and photographic situation. Each stereo image orphotograph is placed on an independent surface that can be moved andtilted in all directions. Projection stereoplotters can. accommodate awider range of photographic situations and camera geometries than thesimple device described earlier, and can more accurately reconstruct themodel of the photographed scene. However, the physical reconstruction ofthe projection stereoplotters results in much more complexity,fragility, and cost than the simple stereo-plotter. Moreover, somefactors such as differential shrinkage of the photographic film aredifficult and expensive to physically reconstruct. Projectionstereoplotters can incorporate only some of these additional factors,and in doing so further increase complexity and cost.

Several stereoplotters do not physically create a stereo scale model ofthe original scene but instead create that model mathematically. Onesuch stereoplotter includes two independent, horizontal, movableplatforms or measuring stages, each of which supports a stereo imagesuch as a stereo-photograph; a binocular optical viewing device forproviding a three-dimensional image for an operator; and a controlcomputer. A measuring half mark is inserted in the optical path fromeach photograph to provide a floating mark in the threedimensionalmodel. Controls are provided for the operator to command apparentmovement of the floating mark through a reconstructed stereo model ofthe photographed scene. The commands are in the form of modelcoordinates, regular three-dimensional coordinates which define thelocation of any point in an accurate, undistorted model of thephotographed scene. The controls generate input signals to a high-speedcomputer. The computer essentially simulates the photographic situationand camera geometry mathematically, performing the geometrictransformations that relate the operator command floating mark locationin the stereo model to the corresponding location on each photograph atwhich the model location was imaged. The photo locations are defined byseparate x, y, z stereo image coordinate systems for each photograph. Asused herein, the z stereo image coordinate is the principal distance ofthe camera, a constant, and the x stereo image coordinate liessubstantially parallel to the base distance of the binocular viewingdevice. After calculating the two image locations, the computer controlsthe movement of each stage with respect to the half marks so that thecalculated image location is placed directly beneath the half marks asviewed through the optics.

The above-described stereoplotter possesses a number of advantages overthe conventional opticalmechanical projection stereoplotters. Forexample, the computer can be designed or programmed to eliminateinaccuracies caused by such factors as differential film shrinkage, lensdistortion, and any other systematic physical phenomenon that can bemathematically modeled. However, this stereoplotter has a majordisadvantage in that a fast and sophisticated computer is needed topermit the operator to command floating mark movements through thereconstructed model. The computer must be used continuously duringplotting and must process each and every operator input signalinstantaneously in order to have the floating mark appear to movethrough the stereo image in direct response to the operator's commands.The fact that such a computer must be an integral part of thisstereoplotter, and that no plotting can be done without the immediateoperation of the computer, makes the stereoplotter a complex andexpensive device.

Another stereoplotter is known that creates an undistorted contour mapof a scene mathematically from a model of the scene that may bedistorted. This stereoplotter includes apparatus for holding and viewingtwo stereo images to provide a three-dimensional model for an observer.The floating mark in this stereoplotter comprises a small disc that ismounted on a mechanical motion device to be moved in the X, Y, and Zdirections in space from point to point in the threedimensional model.The stereoplotter also includes apparatus for mechanically measuring thecoordinate positions of the floating mark in the three-dimensionalmodel, and a computer connected to receive the measured X, Y, and Zmodel coordinates of points in the model and to calculate the coordinatepositions of those points in an undistorted contour map of the scene.

This stereoplotter possesses a number of advantages in that the computercan be designed or programmed to provide an extremely accurate map ormodel of a photographed scene. However, it also possesses some verysignificant disadvantages in that a large number of mathematictransformations that relate positions in the distorted model topositions in the scene must be determined and supplied to the computerbefore an operator can begin plotting or selecting points of interestwith this device. It is extremely difficult and time consuming to obtainthese transformations. In addition, because the computer is an integralpart of the stereoplotter that is adapted to continually calculate thepositions of all points in the actual scene or an undistorted scalemodel of that scene as the floating mark is moved in the distortedmodel, this stereoplotter is also an expensive device.

All previous stereoplotters are based on the requirement of firstreconstructing the photographed scene stereoscopically as well aspossible within the design limitations of the plotter, and thenextracting the dimensional information desired from the reconstructionwhile making floating mark movement commands in object or scaled objectcoordinates. Some stereoplotters do this reconstruction well, somepoorly, but the intent is the same.

SUMMARY OF THE INVENTION The subject invention comprises a method andapparatus for calculating the coordinate positions in an actual scene orin a scale model of that scene of points selected from athree-dimensional image of that scene. As used herein, the termthree-dimensional image defines a collection of image points with eachimage point formed from one conjugate point on each of two stereoimages. Unlike prior art systems, the threedimensional image from whichpoints of interest are selected need not be an accurate or undistortedrepresentation of the actual scene. The operator can select points froma distorted image of that scene. Therefore, only a minimum amount ofpreliminary orientations of the two stereo images must be performedbefore an operator can start recording points of interest. Theorientation of the two stereo images during recording need notcorrespond to the orientation of those images during their formation.The stereo images need only be sufficiently oriented with respect toeach other during plotting to permit an operator to stereoscopicallyselect points of interest. Also unlike the prior art systems, the

' image positions of conjugate point pairs on the stereo images formingpoints of interest in the threedimensional image, rather than thepositions of the points themselves in the coordinate system of thethreedimensional image, are recorded and used to calculate thecoordinate positions of the selected points in either an undistortedmodel of the scene or in the scene itself.

Several stereoplotters illustrating numerous novel features of thisdimension are illustrated herein. Each of the illustrated stereoplottersincludes apparatus for providing a three-dimensional image or model of ascene from two stereo images of that scene. This apparatus includesimage carriers for holding the two stereo images, and a binocularviewing apparatus that allows an operator to view the two stereo imagessimultaneously and thus see a three-dimensional image of the scene. Theillustrated stereoplotters are constructed so that an operator canprovide a relative movement between the binocular viewing apparatus andthe two stereo images so that he can view and select points of interestfrom various areas of the three-dimensional image.

The two image carriers are also constructed so that they can be movedrelative to each other. The character of the model viewed by an operatoris unimportant because only the image positions of conjugate point pairsare used to create the undistorted model of the scene. An operator canthus move the two stereo images to provide comfortable stereo fusion inthe area of the three-dimensional image in which he is selecting pointsof interest when he moves from one area of the three-dimensional imageto another during plotting.

A novel grid structure is incorporated into each image carrier toprovide a reference measuring coordinate system for measuring thecoordinates of conjugate points on the stereo image. The image positionsof conjugate points are first measured in the coordinate systems of thetwo grids. The grid coordinates of conjugate point pairs forming allpoints of interest can be recorded before determining the relationshipbetween the coordinate systems of the two grids (grid coordinates), thecoordinate systems of the two stereo images (stereo image coordinates),and the coordinate system of the actual scene or a scale model of thatscene (model coordinates). The two stereo images are securely fastenedto the two grids so that the orientation between the stereo images andthe grids remains fixed while all points of interest are being selectedand recorded. The relationship between the grid coordinate system andthe stereo image coordinate system is determined by recording the gridcoordinates of special reference marks whose stereo image coordinatesare known and calculating the transformation factors required to convertthe measured grid coordinate values to the known stereo image coordinatevalues. The relationship between the stereo image coordinate systems andthe model coordinate system is similarly determined using points in thescene whose model coordinates are known. However, the calculation of thetransformation between the grid coordinate systems and the stereo imagecoordinate systems, and between the stereo image coordinate systems andthe model coordinate system, as well as the calculation of thecoordinate positions in an undistorted model of the scene can beperformed after the grid coordinates for conjugate point pairs formingall points of interest have been recorded. It is thus not necessary tohave or use a computer while points of interest are being selected fromthe possibly distorted three-dimensional image used by the operator.

One stereoplotter illustrated herein includes a feedback system thatallows an operator to select and record points on a contour in theactual scene even though he is selecting those points from athreedimensional image of the scene that may be distorted. Thisstereoplotter includes a binocular viewing apparatus and a floating markassociated with that viewing apparatus that an operator uses to selectand identify points of interest in the three-dimensional scene. In thisstereoplotter, the model coordinate position of each selected point ofinterest is calculated immediately after the recording of the gridcoordinates of the conjugate point pair forming that selected point.Calculated grid coordinate adjustments are supplied to a feedbackcontrol system constructed to move out of the stereo images and therebyintroduce observable X parallax into the three-dimensional image viewedby the operator when the calculated elevation of a point differs fromthe elevation of a preselected contour of the scene. The operatorprovides a relative movement between the stereo images and the viewingapparatus to eliminate this X parallax and thereby causes the floatingmark to be moved toward a point whose calculated elevation in the modelcoordinate system will be on the preselected contour.

Novel half marks are also illustrated herein that can be used witheither of the two illustrated stereoplotters. These half marks permit anoperator to record the x and y coordinates of conjugate points from onestereo image and only the x coordinates of conjugate points on the otherstereo image, and to use these three coordinate values of conjugatepoints to calculate the coordinate positions of selected points in anundistorted model of the scene. These novel half marks are showninserted into each optical path of the binocular viewing apparatus ofone stereoplotter .to provide a floating mark for selecting andidentifying points of interest in the three-dimensional image. The twohalf marks are superimposed on each other when placed over conjugateimage points and viewed by an operator. The half marks provide afloating mark having both x coordinate and y coordinate definingportions so that an operator can select and identify points of interestin the threedimensional image. However, because one half mark providesonly an x defining portion of the floating mark, the floating mark willnot appear to separate into two distinct marks when the half marks areplaced over conjugate points of the two stereo images and when the twostereo images are so oriented with respect to each other that there is asmall amount of Y parallax in the three-dimensional image viewed by theoperator. This half mark design thus minimizes the adjustment necessarywhen recording points of interest in different areas of a distortedthree-dimensional image. That is, an operator need not readjust thestereo images to remove small amounts of Y parallax from the portion ofthe three-dimensional image that he is viewing.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features andadvantages of this invention, which are defined by the appended claims,will become apparent upon a consideration of the following descriptionand accompanying drawings in which:

FIG. 1 is a schematic diagram of an embodiment of the stereo-plotterapparatus of this invention;

FIG. 2 is a cutaway schematic view of the binocular viewing apparatus ofthe stereoplotter shown in FIG. 1;

FIG. 3 is a perspective view of two images of a land area taken fromdifferent vantage points which illustrate that the coordinates of apoint on the land area can be determined from the x and y stereo imagecoordinates of that point on one image and the x stereo image coordinateof that point on the other image;

FIG. 4 illustrates several combinations of half marks designed forobtaining x and y coordinate information from one stereo image and xcoordinate infonnation from the other; and

FIG. 5 is a schematic view of another embodiment of the stereo-plotterapparatus of this invention constructed to provide a signal for anoperator that notifies him that he is recording points displaced from apreselected contour in the three-dimensional scene represented by thestereo images.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a stereoplotter10 including apparatus 12 for holding two stereo images 14 and 16 whichare photographs of a scene, and binocular viewing approviding a recordof the grid coordinates of conjugate points on the stereophotographs l4and 16 forming points in the three-dimensional image selected to be ofinterest by an operator. The apparatus 20 supplies the recorded gridimage coordinates to calculating apparatus 22 which is adapted to usethe recorded coordinates to calculate first the stereo image coordinatesof the conjugate point pairs, and from these the coordinate position inan undistorted model of the scene of each three-dimensional image pointrepresented by a recorded pair of conjugate points. The calculated modelcoordinate positions provided by calculating apparatus 22 are suppliedto agraphic output device 23 which provides a two-dimensional graphicrepresentation of the undistorted scene.

The apparatus 12 for holding the two stereophotographs 14 and 16includes a first surface or platform 24, movably mounted on table 26 bycasters 28. Flatform 24 is mounted so that it can be moved relative tothe viewing apparatus 18 so that an operator can view and record pointsof interest in various portions of the three-dimensional image providedby the two stereo images 14 and 16. Platform 24 is held by a parallelmotion arm 26 that forces platform 24 to remain parallel with the X axisof the stereo-plotter 10 during any platform movement. This prevents anoperator from inadvertently moving the platform 24 in a manner thatwould cause Y parallax to be introduced into the threedimensional imageprovided by the stereophotographs l4 and 16. The platform 24 isconnected to a captive ball 30 which an operator moves to move the twostereophotographs l4 and 16 with respect to the viewing apparatus 18. Aframe 32 surrounds thecaptive ball 30 and acts as a guide that preventsthe operator from moving the platfonn 24 so far in one direction thatthe stereo images 14 and 16 will no longer be aligned with the viewingapparatus 18.

Two platforms 34 and 36 are movably mounted on the first platfonn 24.Platform 34 holds the stereophotograph 14 while platform 36 holdsstereophotograph 16, and a sheet of drawing paper 38. A rectractablymounted pencil 40 forms a trace on drawing paper 38 of the relativemovement of the stereophotograph 16 with respect to the viewingapparatus 18. This trace prevents an operator from inadvertently viewingand recording the coordinates of one point, line, or area of interestmore than once. A rack and pinion 42 is provided to move platform 34 andstereophotograph 14 along the Y axis of stereoplotter l0, and a secondrack and pinion 44 is provided to move platform 36 and stereophotograph16 along the X axis of stereoplotter 10. An operator moves the twostereophotographs with these two racks and pinions to so orient themrelative to one another that they provide a three-dimensional image thatcan be comfortably viewed and from which he can select points ofinterest to be recorded.

The operator sees a three-dimensional image by viewing the twostereophotographs l4 and 16 through two eyepieces 46 and 48 of theviewing apparatus 18. These two eyepieces determine the eye base and theorientation of the X, Y, and Z axes of the stereoplotter 10. The eyebase of the stereoplotter 10 is a line connecting the centers of the twoeyepieces 46 and 48. The X axis of the stereoplotter is parallel to thiseye base. The Y axis of the stereoplotter is perpendicular to the X axisand is substantially in the plane of the stereo images 14 and 16. The Zaxis of the stereoplotter defines elevation in the three-dimensionalimage viewed by an operator and is perpendicular to both the X and Yaxes, and is also substantially normal to the plane of the stereo images14 and 16.

A detailed view of one path of a binocular viewing apparatus 18 isprovided by the cutaway view of FIG. 2. The path between eyepiece 48 andstereophotograph 16 includes a prism 49 referred to by those skilled inthe art as a Frankfort Arsenal Prism No. 4, a glass surface 50, mirrors52 and 54, and a glass surface 56 hav ing a half mark 58 etched thereon.The half mark 58 is placed over stereo image 16. A second half mark 62(FIG) 1) is placed over stereo image 14. These two half marks form afloating mark in the threedimensional image viewed by the operator whenthey are placed over conjugate points on the two stereophotographs. Thefloating mark formed by these two half marks appears to move in thethree-dimensional image viewed by an operator as the platform 24 ismoved relative to the viewing apparatus 18. An operator selects pointsof interest in the three-dimensional image stereoscopically by movingthe platform 24 to place the floating mark over those points.

The viewing apparatus 10 also includes a mirror 60 which an operator canposition to superimpose an image of the trace pattern on sheet 38 ontothe image of the scene provided by stereo image 16. He can thus view thetrace pattern of the previous relative movement of the viewing apparatus18 and stereophotographs 14 and 16 as he views the three-dimensionalimage provided by those stereophotographs.

The grid coordinates of conjugate points forming points of interest inthe three-dimensional image viewed by an operator are provided by theapparatus 20 which is constructed to provide a record of the positionsof the two half marks 58 and 62. Any number of devices are known thatcould be used to determine the positions of these two half marks.However, the particular apparatus shown comprises the coordinatedetermining apparatus described in the U.S. Pat. Application Ser. No.805,559, Automatic Coordinate Determining Device, K. V. Bailey; assignedto The Bendix Corporation. This apparatus includes two conductive gridstructures 64 and 66 that are fixedly attached to photographs 14 and 16,respectively, and two conductive cursors 68 and 70 which surround thehalf marks 62 and 58, respectively. The center of each half mark islocated at the center of the cursor surrounding it. Signal generatingapparatus 72 transmits signals to the two cursors 68 and 70 which causesignals to be induced in the conductive grid structures 64 and 66. Theseinduced signals change in response to relative movement between gridstructures 64 and 66, and the cursors 68 and 70. The induced signals aretransmitted to signal processing apparatus 74 which is constructed to beresponsive to changes in the induced signals to determine the positionsof the centers of cursors 68 and 70 with respect to preselectedreference points on grid structures 64 and 66, respectively. The signalprocessing apparatus 74 transmits signals indicating the positions ofcursors 68 and 70 to recorder 76. Since the half marks 58 and 62 arelocated at the centers of cursors 70 and 68, respectively, these signalsrepresent the positions of the two half marks. Recorder 76 forms arecord of the grid coordinates of the conjugate points forming points,lines, and areas in the three-dimensional image selected to be ofinterest by an operator. Signals from recorder 76 are transmitted tocalculating apparatus 22 which is adapted to calculate the coordinatepositions in an undistorted model of the scene of each point representedby a recorded pair of conjugate points. The information provided bycalculating apparatus 22 is supplied to a plotting device 23 whichprovides an undistorted map or graph of the scene. The nature of thecalculations performed by apparatus 22 and the type of output providedby that apparatus are determined by control or command signals that anoperator inserts into the record provided by recorder 76 with a controldevice 78. Signals from the control device 78 indicate theclassification of the various recorded signals. These signals thusdistinguish one class of recorded points such as f1- ducial marks from asecond class of recorded points such as contour levels, from a thirdclass such as a particular topographic feature.

Although calculating apparatus 22 is shown as connected to the recorder76 in FIG. 1, it is understood that it need not be physically connectedto that apparatus during the time that an operator is viewing the twostereo images 14 and 16 and recording the grid coordinates of conjugatepoints of interest. A record of the grid coordinates of all suchconjugate points can be formed before any calculations need beperformed.

In operation, two stereophotographs l4 and 16 are first placed on andfastened to the grid structures 64 and 66, respectively. Thesephotographs are then moved together with their respective gridstructures either by hand or by use of the rack and pinion structures 42and 44 so that they will be oriented with respect to the binocularviewing apparatus 18 to provide a threedimensional image that can becomfortably viewed by an operator, and from which he can select pointsof interest to be recorded. A record of the grid coordinates ofconjugate points of interest on the two photographs 14 and 16 isprovided by the apparatus 20. As described above, the signal processingapparatus 74 provides signals indicating the positions of the cursors 62and 58 with respect to the grid structures 64 and 66, re-

spectively. Points on the photographs 14 and 16 will generally not havethe same (x and y) coordinate values in both the stereo image coordinatesystems and the grid coordinate systems because the photographs willgenerally be rotated and translated with respect to the grid structures.A transformation between the two systems is made for a photograph byusing the half mark to record the grid coordinates of several fiducialmarks or special reference marks at the edges of the photographs. Theimage coordinates of the fiducial marks are predetermined cameraconstants for the photographs, and are thus known. An operator transmitsa signal from control device 78 to recorder 76 when the floating mark ison a fiducial mark that indicates that the coordinates are those of afiducial mark and can be used to determine the relationship between thegrid and stereo image coordinate systems. The transformation between thetwo coordinate systems is determined by the following equations:

where:

x, y stereo image coordinates of a point x y, grid coordinates of thesame point x y, stereo image coordinates of the gridcoordinate originangle of rotation between the grid and stereo image coordinate systemsAll mathematic symbols defined herein will be used consistentlythroughout and will not be redefined. By inserting the known stereoimage coordinates and the measured grid coordinates for two or morefiducial marks into equations l two or more sets of equations are formedwhich when solved determine the three unknown parameters 0, x,,, and ySeparate grid-to-stereo image coordinate transformations are obtainedfor each stereo image. After the transformations have been determined bythe calculating apparatus 22, the grid coordinates of conjugate imagepoints are converted to stereo image coordinates, using equations (1 Thestereophotographs l4 and 16 are firmly attached to the grid structures64 and 66, respectively, so that the transformation factors 0, x and yneed be calculated only one time for each photograph.

An operator then views the three-dimensional image provided by the twophotographs 14 and 16 and provides a record of the grid coordinates ofconjugate points forming points of interest in the three dimensionalimage. The signal processing apparatus 74 continually provides signalsindicating the positions of half marks 62 and 58. When the operator seesthe floating mark on a point of interest he transmits a control signalfrom the control device 78 to the recording apparatus 76 which directsthat a record be formed of the grid coordinates of the conjugate pointsforming that point of interest. If this point of interest is at thebeginning of a pattern that the operator wishes to trace, such as at thebeginning of a road, river, profile, or contour level, he may alsotransmit a signal from the control device 78 to recorder 76 directingthe grid coordinates of all subsequent positions of the half marks 62and 58 also be recorded, until the operator transmits a terminationsignal from the control device 78. The operator may also supply acontrol signal from control device 78 indicating the type of landmarkbeing followed. This signal is useful for constructing a map or graph ofthe scene.

The recorded sets of grid coordinates for the half marks 62 and 58 aretransmitted to the calculating apparatus 22. This calculating apparatusis adapted to use these recorded grid coordinates to calculate thestereo image coordinates, and then the position in an undistorted modelof the scene of each image point represented by a recorded pair ofconjugatepoints. The stereo image coordinates of conjugate points in thestereophotographs differ from the coordinates in an undistorted model ofthe scene of the points represented by a conjugate point pair forseveral reasons. First, height or elevation of an object in a photographappears as an x,y displacement on that photograph. Second, the image orstereophotograph may be at a different scale from the model. And third,the origin of the stereo image coordinate system for each photograph maybe displaced from the coordinate origin of the model. That is, if thecamera was tilted or rotated slightly when either photograph was taken,the stereo image coordinate system for that photograph will be similarlytilted or rotated with respect to the coordinate system of theundistorted model.

The transformation between stereo image and model coordinates is basedon the recorded grid coordinates of various control point images on thestereophotograph. Control points are photo-identifiable locations in aphotographed scene whose X, Y, and Z coordinates in that scene or in anundistorted model of that scene are known. The operator records the gridcoordinates of the control points on each photograph by pointingstereoscopically with the floating mark to. the control point images andby transmitting control signals from control device 78 to recorder 76which indicate that the half marks are placed over control points on thetwo photographs and identify the control point by number. The gridcoordinates of the conjugate points forming the control point image arethen recorded and transformed to the image coordinates of those pointsaccording to equations (1). Image coordinates of a point are transformedto the model coordinates or the coordinate position of that point in anundistorted model using the following equations: I

x,,,, y',,,, z The stereo image coordinates of photograph l6 rotated tobe parallel to the model coordinate axes by the mathematic expressions:

in which:

X Z The X and Z model coordinates of the image-coordinate origin forstereophotograph 14 x y Stereo image coordinates of the model point(X,Y,Z) as imaged on stereophotograph 14 x y Stereo image coordinates ofthe model point (X,Y,Z) as imaged on stereophotograph 16 c and c Knowncamera constants comprising the perpendicular distances from theperspective centers of the camera lenses to the film planes for thecameras that exposed stereophotographs l6 and 14, respectively (aWell-known direction cosines of 0. (p

which indicate the sequential rotations between the x, y, and z axes ofthe image coordinate system of stereophotograph l6 and the X, Y, and Zaxes of -the model coordinate system.

The (a,,) terms can be expressed in one form as:

(air) cos d) cos sin 4), sin 0, sin

(a,,) cos qS sin sin sin Q cos (a cos fl sin (an) cos 9 cos (23) Sin re(a sin 5 cos cos da sin Q sin (an) sin da sin cos 4),, sin 9. cos

( n) cos #18 C08 16 (b Well-known direction cosines of Q 115 H whichindicate the sequential rotations between the x, y, and z axes of theimage coordinate system of stereophotograph l4 and the X, Y, and Z axesof the model coordinate system.

The (b terms can be expressedin one form as:

(b cos d) cos sin qb sin 0 sin (b cos d) sin H sin 11; sin (2 cos ar) nSin H (b sin dz cos cos sin 0 sin H (b,,) sin 4),, sin H cos d) sin 0cos H aa) C05 #14 cos n The transformation between stereo image andmodel coordinates is determined by inserting the measured stereo imagecoordinates and the known model coordinates of three or more controlpoints into the above equations and solving for the lateraltransformation ele ments L 1 r. and XL, r. and for the angulartransformation elements 0 15 0 d) and K14. Once these transformationelements have been determined, equations (2) can be used to calculatethe position in an undistorted model of the scene, of each pointrepresented by a recorded pair of conjugate points.

Since the positions in an undistorted model of the scene of pointsselected to be of interest by an operator are calculated in acalculating operation that can be entirely independent from theselection of points from the three-dimensional image, the stereoplotter10 can be used to provide a contour map without requiring the operatorto follow a contour in the three-dimensional image in order to providethat map. Indeed, the two stereophotographs l4 and 16 can provide athreedimensional image that is so warped with respect to the actualscene that an operator cannot follow even as approximation of a contourline in the actual scene. An operator may follow a predetermined patternand record points at regular intervals in areas of surface relief andobtain a contour map by allowing calculating apparatus 22 to determinewhich of the recorded points lie along predetermined contours in theundistorted model of the scene. For example, an operator can move theplatform 24 in a manner that moves the floating mark along a pluralityof parallel lines, and he can record the grid coordinates of eithercritical elevation points on these lines or of points spaced atpreselected fixed intervals on these lines.

FIG. 3 illustrates that it is not necessary to use both the x and ystereo image coordinates of conjugate points on each stereophotograph inorder to calculate the position in an undistorted model of the scenerepresented by a recorded pair of conjugate points. That is, theposition of a point in an undistorted model of the scene can bedetermined if the x and y stereo image coordinates of a conjugate pointon one photograph are known and the x stereo image coordinate of theconjugate point on the other photograph is known. FIG. 3 includes thetwo stereophotographs l4 and 16 and the scene or land mass representedby those photographs. The stereo images 14 and 16 are produced from twonegative images 82 and 84, which in turn are provided by two cameras(not shown) located in the positions defined by stereo image coordinatesystems 86 and 88. The coordinate origin of coordinate system 86 definesthe position of the camera lens during formation of negative 82, and thecoordinate origin of coordinate system 88 defines the position of thecamera lens during formation of negative image 84. Any positivephotographic image such as either photographic image 14 or 16 comprisesthe projection of a negative image such as image 82 or 84 through thecamera lens as is shown in FIG. 3.

As FIG. 3 illustrates, if the camera constants, such as theperpendicular distance from the camera lens to the plane of the film inthe camera, and the orientations of the cameras at the time of exposureare known or can be calculated, the position of any point such as point90 on land mass 80 can be determined from the x stereo image coordinateof point 90' and the x and y coordinates of the point 90". The points 90and 90" are the imaged representations of point 90 on the photographs l4and 16, respectively. The position, that is the X, Y, and Z coordinates,of point 90 in the land mass is unique determined by the intersection ofplane 92 and object-image ray 94. On the x stereo image coordinate ofpoint 90 on stereophotograph 14 need be known to form plane 92. That is,this plane extends from the origin of stereo image coordinate system 86through all points on stereophotograph 14 having an 1 stereo imagecoordinate value equal to the x stereo image coordinate value of point90'. The object-image ray 94 extends from the coordinate origin ofstereo image coordinate system 88 through point 90" on stereophotograph16. The x and y stereo image coordinates of that point, therefore,uniquely define this ray.

The stereoplotter shown in FIG. 1 can, therefore, be modified todetermine the coordinate positions in an undistorted model of a scene ofpoints selected to be of interest by an operator using only the stereoimage coordinates of conjugate points of interest on one stereo image,and the x and y stereo image coordinates of conjugate points on theother stereo image. The recorder 76 is adapted to provide the x and ygrid coordinates of conjugate points on one stereo image and the 1: gridcoordinates of conjugate points on the other stereo image using thesignals provided by the processing apparatus 74 indicating the positionsof cursors 58 and 62 with respect to the grid structures 66 and 64.These grid coordinate values may then be converted to stereo imagecoordinates by calculating apparatus 22 using equations (1) in a mannersimilar to that described above. If stereophotograph 14 is positionedwith respect to grid 64 such that the x and y,., stereo imagecoordinates differ from x, and y, grid coordinates only by translationsx, and y equations l for stereo image 14 are simply x x x and the y,grid coordinate is not recorded. Alternatively, the x grid coordinatesof grid 64 may be used in lieu of the true x stereo image coordinatesregardless of the orientation of stereophotograph 14 with respect togrid 64. In'this latter case, the x grid coordinate must be translatedto the stereo image coordinate by the quantity x,,. In either event, theX, Y, and Z coordinate positions in an undistorted model of a scene aredetermined from the three stereo image coordinates x y,,,, and x usingthe following equations:

in which:

(d,,) Direction cosines of 0', dz, and indicating the sequentialrotation of the x, y, and 1 image coordinate axes of stereophotograph 16required to place them parallel to the x, y, and 1 image coordinate axesof stereophotograph 14. The angles 0', 1b, and are simply thedifl'erences Q 0 if, the and 14 e res ectively. These direction cosinescan be expressed in one form as:

(d cos cos sin d1 sin 0. sin

(d,,) cos d) sin '30 sin (b' sin (2 cos (d -sin d) cos 0' (d sin cos cosqb' sin 0' sin (11, cos 4; cos 0' The relationship between the imagecoordinate system for each photograph and the coordinate system of theundistorted model is determined using equations (3) in a manner similarto that described above using equation (2). That is, the stereo imageand model coordinates of control points are inserted into equations (3)which then are solved for the elements of those equations which indicatethe lateral and rotational transformations between the image and objectcoordinate systems. That is, equations (3) are solved for the angulartransformation elements .0 4;,6, Q, and K and the lateral transformationelements X Y Z (X -X and (Z Z Once these transformation elements areknown, equations (3) are used to convert the stereo image coordinates ofall selected points to the model coordinates of those points.

Since the x and y stereo image coordinates of conjugate points on onestereophotograph and only the x stereo image coordinates of conjugatepoints on the other stereophotograph are used to determine the positionsof points in an undistorted model of the scene, the two half marks canbe designed so that it will be unnecessary to continually adjust thestereophotographs to remove Y parallax from the three-dimensional imageviewed by the observer. That is, the two half marks 58 and 62 need notbe identical. Several designs for these half marks are shown in FIG. 4.The two half marks must be designed to form a floating mark that anoperator can use to stereoscopically select points of interest.

That is, the floating mark must define a unique x and y position in thethree-dimensional image. However, each half mark need not provide bothan x coordinate and y coordinate defining portion of the floating markbecause only the x coordinates of points on one stereophotograph will berecorded. FIG. 4 illustrates four half marks 95, 96, 98, and 100, thatwill provide both an x and a y defining portion of the floating mark,and four half marks 102, 104, 106, and 108 that provide only an xcoordinate defining portion of that floating mark. Any one of the marksthrough can be used with any one of the marks 102 through 108 to providea floating mark that an operator can use to identify and select pointsin a three-dimensional image. One of the marks 95 through 100 would beplaced over the stereophotograph from which it is desired to record boththe x and y grid coordinates of conjugate points of interest, and one ofthe half marks, 102 through 108 would be placed over thestereophotograph from which it is desired to record only the x gridcoordinates of conjugate points of interest. An operator will see thetwo marks superimposed on each other so that they will appear to fusetogether to form a floating mark. The half marks will not appear toseparate when placed over conjugate points on stereo images oriented toprovide a three dimensional image having Y parallax. The cross patternof the half mark selected from marks 95 through 100 will merely appearto move along the line comprising the half mark selected from marks 102through 108 in response to the introduction of l parallax into thethree-dimensional image. Half marks 104 through 108 do provide ay-reference for an operator, should he desire to record a y coordinate.This y-reference is present as one or more breaks in the lines. Thebreaks provide y coordinate information when those lines are viewed byone eye alone.

The advantage of this design is due to the physiology of human viewing.If two conjugate images viewed through the optics of the device areslightly separated in the Y direction, the eyes can accommodateadequately and so maintain stereo fusion. lf conventional half mark dotsare used, when their Y separation is different from that of theconjugate image areas, they are not over conjugate points, and theoperator notes 1 parallax. Hence, this Y accommodation capability doesnot help him; he still must turn the Y-adjustment apparatus 42 to removethe Y parallax he sees in the marks. With the new mark design, thefloating mark is not defined in the Y direction, hence the operator seesno Y parallax under such condition of photograph displacement in the Ydirection. Instead, the X-segment of the cross appears to lieperpendicular to the floating line at some point other than the centerof the floating line. The operator need only translate the entirereference surface in Y to point to an image with the mark. Thus,differential adjustment of the half marks in the Y direction to remove Yparallax need be made much less frequently than when using conventionalhalf mark patterns, only when the Y parallax becomes too great forstrain-free Y accommodation of the eyes or when the X-segment of thecross moves beyond the end of the floating line.

FIG. 5 illustrates a stereoplotter 110 that is constructed to allow anoperator to select points from the model that lie along a contour in theactual scene. The stereoplotter 110 includes a feedback circuitcomprising a control 114 and motor 116 for moving rack and pinion 44 anda feedback signal generator 117 that indicates the amount of movementprovided by motor 116. This feedback circuit receives the calculatedcoordinates of positions provided by calculating apparatus 22 andprovides a signal to an operator which indicates whether or not he isselecting points that lie along a preselected contour in the undistortedmodel. The operator is able to select points along this contour eventhough he is not provided with an unwarped image of that scene.Therefore, in order to provide this signal which indicates whether ornot the operator is following a preselected contour, the relationshipbetween grid coordinates, stereo image coordinates, and the coordinatesystem of the undistorted model is determined before plotting is begunby placing the half marks 58 and 62 over fiducial marks and controlpoints on the two stereo images and calculating the relationshipsbetween the several coordinate systems in the manner described above.The calculating apparatus 22 is then adapted to calculate the positionin an undistorted model of a scene of each point represented by arecorded pair of conjugate points immediately after the recording of thegrid coordinates ofthe conjugate point pair.

These calculated positions are transmitted to the control device 114which causes X parallax to be introduced into the three-dimensionalimage viewed by the operator when the calculated elevation of a pointdiffers from the elevation of a preselected contour.

In order to obtain this introduction of X parallax from thethree-dimensional image, control apparatus 114 is adapted to determinethe difference between the calculated elevation ofa point and a contourelevation previously entered by the operator by control signals fromcontrol device 78. Control apparatus 114 causes stereophotograph 16 tobe moved in a direction determined by the direction of the elevationerror. lf the calculated elevation of a point is lower than thepreselected contour elevation, the stereophotograph 16 is moved awayfrom stereophotograph 14. Similarly, if the calculated elevation of apoint is higher than the preselected contour elevation, stereophotograph16 is moved toward stereophotograph 14. The amount of movement ofstereophotograph 16 in each case is proportional to the elevation errorbetween the point and the preselected contour elevation. The movement ofstereophotograph 16 is provided by motor 116 which drives rack andpinion 44 to move carrier 36 and thus the stereophotograph 16 and grid66 placed thereon. Generator 117 generates feedback signals for control114 to indicate the amount of movement provided by motor 116. Control-114 will continue to cause stereophotograph 16 to be moved until thatcontrol receives sufficient signals from signal generator 117 indicatingthat the stereophotograph has been moved a distance appropriate with themagnitude of the elevation error.

The presence of a slight X parallax in the threedimensional image viewedby the operator is seen as the floating mark appears to float above orburrow beneath the surface of the three-dimensional image. Thiscondition indicates to him that he is selecting and recording pointsfrom the three-dimensional image that are slightly displaced from thepreselected contour in the undistorted model of the scene, and that hemust correct this condition by adjusting the platform 24 with thecaptive ball 30 to make the floating mark appear to resume contact withthe surface of the threedimensional image. By providing error indicatingsignals to control apparatus 114 at sufficiently frequent intervals,calculating apparatus 22 insures that the elevation errors are alwayskept within acceptably small limits. Thus, since the calculatedpositions are also transmitted to the graphical output device 23,stereoplotter provides an undistorted contour map of a scene withoutrequiring that the two stereo images be so oriented to provide anundistorted threedimensional image of a scene before an operator canbegin recording coordinates.

It is also understood that the control device 114 could provide theelevation signal in a different manner, by lighting one of two displaylamps to indicate a plus or minus elevation error, the direction of eacherror being indicated by a different colored lamp. In this case themotor apparatus 116 is not used. The lamps are located on the equipmentso the light is visible to the operator as he observes thethreedimensional model through the binocular viewing apparatus. Headjusts the X parallax or floating mark location manually, so as to keepthe floating mark in contact with the perceived surface of thethreedimensional image at a location where neither error lamp is lit.

Having thus described several embodiments of this invention, a number ofmodifications will be immediately obvious to those skilled in the art.Therefore,

What is claimed is:

1. A stereoplotter for providing an undistorted model of a scene fromtwo stereo images of the scene each stereo image including referencepoints representing predetermined locations in the scene comprising:

means for holding the two stereo images of the scene in positions thatprovide one viewing the two stereo images with a three-dimensional imagethat may be either distorted or undistorted, said threedimensional imagecomprising a collection of image points, with each image point formedfrom one conjugate point on each of the two stereo images;

viewing means for viewing various points, lines, and

areas of said three-dimensional image;

means for selecting individual points and series of points defininglines and areas of interest in said three-dimensional image;

means for automatically measuring the image positions of conjugate pointpairs forming said selected image points, lines and areas in saidthreedimensional image;

calculating means for using said measured image positions and therelationship between the positions of said reference points on thestereo images and the predetermined locations in the scene to calculatethe coordinate positions in an undistorted model of said scene of imagepoints, lines and areas represented by said selected pair ofconjugatepoints; and

output means responsive to said calculated coordinate positions forproviding a representation of the undistorted scene.

2. The stereoplotter set forth in claim 1 in which:

the stereoplotter further includes means for recording said measuredimage positions; and

said calculating means comprises means for calculating said coordinatepositions in said undistorted model for each selected point after allpoints of interest have been selected and recorded.

3. The stereoplotter set forth in claim 1 in which said calculatingmeans comprises means for responding immediately to said measured imagepositions and provide a real time representation of the coordinateposition of each selected image point, line, and area in an undistortedmodel of the scene.

4. The stereoplotter set forth in claim 1 further including:

means for recording said measured image positions;

and

a control device for inserting control signals into the record of saidimage positions to indicate the classification of said recorded pointpairs.

5. The stereoplotter set forth in claim 1 in which:

said means for selecting points, lines, and areas of interest comprisesmeans for providing a floating mark to stereoscopically identify andselect points, lines and areas of interest in said three-dimensionalimage; and

the stereoplotter further includes means for automatically recording theimage positions of conjugate point pairs forming an image pointidentified by the floating mark whenever said floating mark is moved apredetermined distance.

6. The stereoplotter set forth in claim 11 further including means forforming a trace of points, lines, and

areas selected to be of interest to enable an operator to determine thepoints, lines, and areas of interest that have been selected.

7. The stereoplotter set forth in claim 6 in which: said viewing meansis constructed to superimpose an image of said trace onto saidthree-dimensional image.

8. In a stereoplotter for providing an undistorted model of a scene fromtwo stereo images of the scene carrying reference points representingpredetermined locations in the scene and having:

means for holding the two stereo images; and

viewing means for viewing the two stereo images to provide a possiblydistorted three-dimensional image of said scene, saidthree-dimensional'image comprising a collection of image points, eachimage point formed from one conjugate point on each of the two stereoimages; and

means for selecting image points defining lines and areas of interest insaid three-dimensional image;

the improvement comprising:

means for providing a first coordinate measuring system for one of saidstereo images and a second coordinate measuring system for the other ofsaid stereo images;

measuring means for measuring the coordinate positions in saidcoordinate measuring systems of conjugate points on said two stereoimages forming. a selected image point;

calculating means for using said measured positions and the relationshipbetween the positions of said reference points in said coordinatemeasuring system and the predetermined locations in the scene tocalculate the positions in an undistorted model of the scene of points,lines and areas represented by measured pairs of conjugate points; and

means for moving said one stereo image and firstcoordinate system withrespect to said other stereo image and second coordinate system to varythe stereo quality and provide stereo fusion in the area of thethree-dimensional image being viewed.

9. The stereoplotter set forth in claim 8 in which:

said means for providing said first coordinate measuring systemcomprises a first grid device;

said means for providing said second coordinate measuring systemcomprises a second grid device; and

said stereoplotter also includes:

calculating means for converting said coordinate positions in saidcoordinate measuring systems to the stereo image coordinates of saidconjugate points and for using said stereo image coordinates tocalculate the coordinate positions in an undistorted model of the sceneof said selected image points.

10. The stereoplotter set forth in claim 9 in which:

said one stereo image is fastened to said first grid device and saidother stereo image is fastened to said second grid device to maintain afixed relationship between each stereo image and the coordinate systemprovided by the grid device fastened to that stereo image; and

said means for holding two stereo images comprises a first image carrierfor holding one stereo image and a second image carrier for holding theother stereo image.

11. The stereoplotter set forth in claim 10 in which said one stereoimage and first grid device are movably disposed on said first imagecarrier, and said other stereo image and said second grid device aremovably disposed on said second image carrier to permit an operator tomove said stereo images with respect to said image carriers.

12. The stereoplotter set forth in claim 8 in which:

said viewing means comprise binocular viewing apparatus for viewing saidtwo stereo images simultaneously, said binocular apparatus defining aneye base for the stereoplotter; and

said means for moving comprises means for moving one of said stereoimages in a direction parallel to said eye base.

13. The stereoplotter set forth in claim l2 in which:

said two stereo images are held substantially in a plane; and

said moving means comprises means for moving one of said stereo imagesin a direction substantially perpendicular to said eye base and in saidplane.

14. in a stereoplotter having:

means for holding two stereo images of a scene; and

viewing means for providing a first optic path to one of said stereoimages and a second optic path to the other stereo image to therebyprovide one viewing the stereo images with a three-dimensional image ofsaid scene, said three-dimensional image comprising a collection ofimage points, each image point formed from one conjugate point on eachof two stereo images;

improved means for providing a floating mark for identifying points ofinterest in said threedimensional image comprising:

means disposed in the first optic path defining a first half mark foridentifying points on the one image shaped to provide both an xcoordinate defining and a y coordinate defining portion of said floatingmark; and

means disposed in the second optic path defining a second half mark foridentifying points of interest on the other of said stereo images shapedto provide only an x coordinate defining portion of said floating mark,said two half marks providing a floating mark capable of identifyingpoints in said three-dimensional image when said stereo images areoriented to provide a three-dimensional image having a moderate amountof Y parallax, and when said half marks are placed over conjugate pointson the two stereo images.

15. The stereoplotter set forth in claim 14 further including:

means for measuring the x and y image positions of identified conjugatepoints on said one stereo image;

means for measuring only the x image positions of identified points onsaid other stereo image; and

calculating means for using said measured image positions tocalculatethe coordinate position in an undistorted model of said sceneof points identified in said three-dimensional image.

16. The stereoplotter set forth in claim 15 in which:

said viewing means comprises binocular viewing apparatus for viewingsaid two stereo images simultaneously, said binocular apparatus definingan x axis for the stereoplotter parallel to the eye base of saidbinocular apparatus; and i said second half mark comprises a brokenstraight line substantially perpendicular to said x axis, said breakdefining a y coordinate position when said second half mark is viewedalone.

17. The stereoplotter set forth in claim 15 in which:

said means for holding said two stereo images is constructed to holdsaid images substantially in a plane;

said viewing means comprise binocular viewing apparatus for viewing saidtwo stereo images simultaneously, said binocular apparatus defining aneye base for the stereoplotter; and

said calculating means comprises means for calculating said coordinateposition in said undistorted model using the formulas:

where:

the X axis of the coordinate system for the above three formulas isparallel to said eye base;

the Y axis of said coordinate system is perpendicular to said X axis andis substantially in said plane; the Z axis of said coordinate system isperpendicular to the X and Y axes;

X,Y,Z the coordinates of a point in the scene;

X Y Z the location in model coordinates of the coordinate origin of theimage coordinate system for one stereo image;

S a scale factor relating image coordinate scale to model coordinatescale; and

x Y z' the stereo image coordinates of the one stereo image with itscoordinate origin at X Y Z rotated to be parallel to the modelcoordinate axes.

18. A stereoplotter for providing coordinate positions of selectedpoints in an undistorted model of a scene, and indicating whether saidpoints lie on a preselected contour in said undistorted modelcomprising:

means for holding two stereo images of the scene;

viewing means for providing a possibly distorted three-dimensional imageof said scene, said threedimensional image comprising a collection ofimage points, each image point formed from one conjugate point on eachof said stereo images;

means for selecting points of interest in said threedimensional image;means for automatically measuring the image positions of conjugate pointpairs forming said selected image points in said three-dimensionalimage;

calculating means for responding immediately to said measured imagepositions and calculating the coordinate position in an undistortedmodel of said scene of said selected image points; and

signal means responsive to said calculated coordinate positions forproviding a signal indicating whether the calculated elevation of aselected point differs from the elevation of a preselected contour, saidsignal providing means thereby enabling an operator to select pointsalong a preselected contour in an undistorted model of the scene from apossibly distorted three-dimensional image of that scene.

19. The stereoplotter set forth in claim 18 in which said signalproviding means provides a first signal to indicate the calculatedelevation of a selected point is higher than said preselected elevationand a second signal to indicate the calculated elevation of a selected'point is lower than said preselected elevation.

20. The stereoplotter set forth in claim 18 in which:

said viewing means comprises a binocular viewing apparatus for viewingsaid two stereo images simultaneously, said binocular apparatus definingan x axis for said stereoplotter parallel to the eye base of saidbinocular apparatus;

said selecting means comprises means for providing a floating mark forselecting points of interest in the three-dimensional image; and

said signal providing means comprises means for moving one of saidstereo images along said x axis of said stereoplotter-to introduce Xparallax into said three-dimensional image to raise the elevation ofsaid floating mark when said calculated elevation is greater than saidpreselected elevation, and to lower the elevation of said floating markwhen said calculated elevation is lower than said preselected elevation.

21. A method for providing an undistorted model of a scene from athree-dimensional image that may be either distorted or undistorted ofthe scene comprising the steps of:

providing two stereo images of a scene, said stereo images carryingreference points representing predetermined locations in the scene;

viewing said two stereo images simultaneously to obtain a possiblydistorted three-dimensional image of said scene, said three-dimensionalimage comprising a collection of image points, each image point formedfrom one conjugate point on each of said stereo images;

selecting points, lines, and areas of interest in said three-dimensionalimage;

measuring the image positions of conjugate point pairs forming saidselected points, line sand areas of said three-dimensional image;

using said measured image positions and the relationship between theimage positions of said reference points and the predetermined locationsin the scene to calculate the coordinate positions in an undistortedmodel of said scene of image points,

lines. and areas represented by measured pairs of conjugate points; and

forming a representation of the undistorted scene from said calculatedcoordinate positions.

22. The method set forth in claim 21 in which said steps of measuringand calculating said positions are performed by automatic measuring andcalculating apparatus respectively, and in which said step of formingsaid representation is performed by an automatic graphing apparatusresponsive to said calculated coordinate positions.

23. The method set forth in claim 21 further including the step of: I

recording said measured image positions; and

said step of calculating coordinate positions in an undistorted model isperformed for each selected conjugate point pair after a record of theimage po sitions of all selected conjugate point pairs has beenprovided.

24. The method set forth in claim 21 in which said step of calculatingcoordinate positions in an undistorted model is performed for eachselected conjugate point pair immediately after selection of said pointpair to provide a real time representation of the undistorted model.

25. The method set forth in claim 21 further including the steps of:

recording said measured image positions; and

inserting control signals into the record of stereo image coordinatesthat indicate the classification of recorded point pairs.

26. The method set forth in claim 21 in which:

said step of selecting points, lines, and areas of interest includesproviding a floating mark to stereoscopically identify and selectpoints, lines and areas of interest in said three-dimensional image; and

the method further includes the step of automatically recording theimage positions of conjugate point pairs forming an image pointidentified by the floating mark whenever said floating mark is moved apredetermined distance. 27. The method set forth in claim 21 in which:said step of selecting points, lines, and areas of interest includesproviding a floating mark to stereoscopically identify and selectpoints, lines, and areas of interest in said three-dimensional image,and moving said floating mark along a plurality of parallel lines toselect points lying along the said lines; and said calculation includesusing the image positions of said selected points lying along said linesto calculate the X and Y model coordinate values of points lying alongpreselected contours of said model at preselected intervals. 28. Themethod set forth in claim 21 further includingthe step of forming atrace of points, lines, and areas selected to be of interest, said traceenabling an operator to determine the points, lines, and areas that havebeen selected.

29. The method set forth in claim 28 further including the step ofsuperimposing an image of said trace onto said three-dimensional image.

30. A method for providing coordinate positions of selected points in anundistorted model of a scene, said points being selected from athree-dimensional image of the scene that may be distorted and that maybe varied during point selection to minimize distortions in one area ofsaid image comprising the steps of:

providing two stereo images of the scene, each stereo image includingreference points representing predetermined locations in the scene;

providing a first coordinate measuring system for one stereo image and asecond coordinate measuring system for the other of said stereo images;

viewing said two stereo images simultaneously to obtain athree-dimensional image of said scene, said three-dimensional imagecomprising a collection of image points, each image point formed fromone conjugate point on each of said stereo images;

selecting points defining lines and areas of interest in saidthree-dimensional image;

measuring the positions in said coordinate measuring systems ofconjugate point pairs forming said selected image points;

moving one of said stereo images with respect to the other whilemaintaining a fixed spatial relationship between each stereo image andthe coordinate measuring system for said each stereo image, saidrelative movement thereby enabling an operator to vary the stereoquality of and provide stereo fusion in the area of thethree-dimensional image being viewed; and

using said measured coordinates and the relationship between thepositions of said reference points in said coordinate measuring systemsand in an undist r e mo e szLtsu sa to calculate theme- 'tions in anundistorted model of the scene of image points represented by measuredpairs of conjugate points.

31. The method set forth in claim 30 in which said step of calculatingcoordinate positions in an undistorted model includes:

determining the relative positions of said one stereo image in saidfirst measuring coordinate system and the relative positions of saidother stereo image in said second measuring coordinate system; and

converting said positions measured in said coordinate measuring systemsto stereo image coordinate positions; and

using said stereo image coordinate positions to calculate positions inan undistorted model of image points represented by measured pairs ofconjugate points.

32. The method set forth in claim 31 in which:

said step of providing first and second reference coordinate measuringsystems comprises fastening a first reference grid measuring system toone of said stereo images and fastening a second reference gridmeasuring system to the other of said stereo images; and

said step of converting coordinate positions in said coordinatemeasuring system to stereo image coordinate positions is accomplishedusing the formulas:

where:

x,y stereo image coordinates of a point x,,,y,, grid coordinates of thesame point x,,,y stereo image coordinates of the grid coordinate originangle of rotation between the grid and stereo image coordinate systems.

33. The method set forth in claim 32 in which:

said step of measuring positions in said coordinate measuring systemscomprises measuring the x and y coordinates of conjugate points on eachstereo image; and

said calculation of the coordinate positions in an undistorted model ofimage points represented by pairs of conjugate image points is performedaccording to the formulas:

where:

the X axis of the coordinate system for the above three formulas isparallel to the eye base of an observer viewing said three-dimensionalimage in an ordinary manner;

the Z axis of said coordinate system is perpendicular to said X axis anddefines elevation in said threedimensional image; 4

the Y axis of said coordinate system is perpendicular to both the X andZ axes;

X ,Y,Z model coordinates of a point in the scene;

X Y Z the location in model coordinates of the coordinate origin of theimage coordinate system for one stereo image;

S a scale factor relating image coordinate scale to model coordinatescale; and

hm 'wJ'w the stereo image coordinates of the one stereo image withcoordinate origin at X YLW r, rotated to be parallel to the modelcoordinate axes.

34. A method for providing coordinate positions of selected points in anundistorted model of a scene, said points being selected from athree-dimensional image that may contain a moderate amount of Y parallaxand be otherwise distorted comprising the steps of:

providing two stereo images of the scene;

viewing said two stereo images simultaneously to obtain a possiblydistorted three-dimensional image of said scene, said three-dimensionalimage comprising a collection of image points, each image point formedfrom one conjugate point on each of said stereo images;

providing a floating mark for selecting and identifying points ofinterest in said three-dimensional image by providing a first half markfor identifying points on one of said stereo images shaped to provideboth x coordinate defining and y coordinate defining portions of saidfloating mark, and a sec- 0nd half mark for identifying points ofinterest on the other of said stereo images shaped to provide only an xcoordinate defining portion of said floating mark, said two half marksproviding a floating mark capable of identifying points in saidthreedimensional image when said stereo images are oriented to provide athree-dimensional image having a moderate amount of Y parallax and whensaid half marks are placed over conjugate points on the two stereoimages;

selecting points of interest in said three-dimensional image with saidfloating mark;

determining the image positions of conjugate points forming saidselected image points; and

using said image positions to calculate the coordinate positions in anundistorted model of said scene of said selected image points.

35. The method set forth in claim 34 in which said second half markcomprises a straight line disposed substantially perpendicular to theeye base of an observer viewing said three-dimensional image in anordinary manner.

36. The method set forth in claim 35 in which said step of providingsaid second half mark provides a broken straight line with said breakdefining a y coordinate position when said second half mark is viewedalone.

37. The method set forth in claim 34 in which:

said step of determining the stereo image coordinates of said conjugatepoints comprises determining the x and y stereo image coordinates ofconjugate points on said one stereo image, and determining the x stereoimage coordinates of conjugate points on said other stereo image; and

said calculating coordinate positions in an undistorted model isperformed using the formulas:

X=XL15+ 10 YL15+ 'y'm Z=ZL16+ m where:

the x axis of the coordinate system for the above three formulas isparallel to the eye base of an observer viewing said three-dimensionalimage in an ordinary manner; the Z axis of said coordinate system isperpendicular to said X axis and defines elevations in thethreedimensional image;

the Y axis of said coordinate system is perpendicular to the X and Zaxes;

X,Y,Z, model coordinates of a point in the scene;

X Y Z the location in model coordinates of the coordinate origin of theimage coordinate system for one stereo image;

S= a scale factor relating image coordinate scale to model coordinatescale and the attitude of one stereo image to that of the other;

Jr',,;,y ,z', the stereo image coordinates of the one stereo image withcoordinate origin at X Y rotated to be parallel to the model coordinateaxes.

38. A method of determining the coordinate posi-' tions in anundistorted model of points selected from a possibly distortedthree-dimensional image of a scene, and for indicating whether saidpoints lie on a preselected contour in said undistorted model comprisingthe steps of:

providing two stereo images of the scene;

viewing said two stereo images simultaneously to obtain a possiblydistorted three-dimensional image of said scene, said three-dimensionalimage comprising a collection of image points, each image point formedfrom one conjugate point on each of said stereo images;

selecting points of interest in said three-dimensional image;

determining the stereo image coordinates of conjugate point pairsforming said selected image points in said three-dimensional image;

using said stereo image coordinates to calculate the coordinate positionin an undistorted model of said scene of an image point immediatelyafter selection of said an image point; and

39. The method set forth in claim 38 in which said step of providing asignal indicating the relationship between said calculated elevation andsaid preselected elevation comprises providing a first signal forindicating said calculated elevation to be greater than said preselectedelevation, and providing a second signal for indicating said calculatedelevation to be less than said preselected elevation.

40. The method set forth in claim 38 in which:

said points of interest in said three-dimensional image are selectedwith a floating mark formed from a first half mark for identifyingpoints on one of said stereo images and a second half mark foridentifying points on the other of said stereo images; and

said providing a signal indicating the relationship between thecalculated and preselected elevations comprises providing a relativemovement between said one stereo image and said one half mark to varythe apparent elevation of said floating mark, said relative movementcomprising movement causing the apparent elevation of said floating markto increase when said calculated elevation is greater than saidpreselected elevation, and to cause the apparent elevation of saidfloating mark to decrease when said calculated elevation is lower thansaid preselected elevation.

1. A stereoplotter for providing an undistorted model of a scene fromtwo stereo images of the scene, each stereo image including referencepoints representing predetermined locations in the scene comprising:means for holding the two stereo images of the scene in positions thatprovide one viewing the two stereo images with a three-dimensional imagethat may be either distorted or undistorted, said three-dimensionalimage comprising a collection of image points, with each image pointformed from one conjugate point on each of the two stereo images;viewing means for viewing various points, lines, and areas of saidthree-dimensional image; means for selecting individual points andseries of points defining lines and areas of interest in saidthree-dimensional image; means for automatically measuring the imagepositions of conjugate point pairs forming said selected image points,lines, and areas in said three-dimensional image; calculating means forusing said measured image positions and the relationship between thepositions of said reference points on the stereo images and thepredetermined locations in the scene to calculate the coordinatepositions in an undistorted model of said scene of image points, linesand areas represented by said selected pairs of conjugate points; andoutput means responsive to said calculated coordinate positions forproviding a representation of the undistorted scene.
 2. Thestereoplotter set forth in claim 1 in which: the stereoplotter furtherincludes means for recording said measured image positions; and saidcalculating means comprises means for calculating said coordinatepositions in said undistorted model for eacH selected point after allpoints of interest have been selected and recorded.
 3. The stereoplotterset forth in claim 1 in which said calculating means comprises means forresponding immediately to said measured image positions and provide areal time representation of the coordinate position of each selectedimage point, line, and area in an undistorted model of the scene.
 4. Thestereoplotter set forth in claim 1 further including: means forrecording said measured image positions; and a control device forinserting control signals into the record of said image positions toindicate the classification of said recorded point pairs.
 5. Thestereoplotter set forth in claim 1 in which: said means for selectingpoints, lines, and areas of interest comprises means for providing afloating mark to stereoscopically identify and select points, lines andareas of interest in said three-dimensional image; and the stereoplotterfurther includes means for automatically recording the image positionsof conjugate point pairs forming an image point identified by thefloating mark whenever said floating mark is moved a predetermineddistance.
 6. The stereoplotter set forth in claim 1 further includingmeans for forming a trace of points, lines, and areas selected to be ofinterest to enable an operator to determine the points, lines, and areasof interest that have been selected.
 7. The stereoplotter set forth inclaim 6 in which: said viewing means is constructed to superimpose animage of said trace onto said three-dimensional image.
 8. In astereoplotter for providing an undistorted model of a scene from twostereo images of the scene carrying reference points representingpredetermined locations in the scene and having: means for holding thetwo stereo images; and viewing means for viewing the two stereo imagesto provide a possibly distorted three-dimensional image of said scene,said three-dimensional image comprising a collection of image points,each image point formed from one conjugate point on each of the twostereo images; and means for selecting image points defining lines andareas of interest in said three-dimensional image; the improvementcomprising: means for providing a first coordinate measuring system forone of said stereo images and a second coordinate measuring system forthe other of said stereo images; measuring means for measuring thecoordinate positions in said coordinate measuring systems of conjugatepoints on said two stereo images forming a selected image point;calculating means for using said measured positions and the relationshipbetween the positions of said reference points in said coordinatemeasuring system and the predetermined locations in the scene tocalculate the positions in an undistorted model of the scene of points,lines and areas represented by measured pairs of conjugate points; andmeans for moving said one stereo image and first coordinate system withrespect to said other stereo image and second coordinate system to varythe stereo quality and provide stereo fusion in the area of thethree-dimensional image being viewed.
 9. The stereoplotter set forth inclaim 8 in which: said means for providing said first coordinatemeasuring system comprises a first grid device; said means for providingsaid second coordinate measuring system comprises a second grid device;and said stereoplotter also includes: calculating means for convertingsaid coordinate positions in said coordinate measuring systems to thestereo image coordinates of said conjugate points and for using saidstereo image coordinates to calculate the coordinate positions in anundistorted model of the scene of said selected image points.
 10. Thestereoplotter set forth in claim 9 in which: said one stereo image isfastened to said first grid device and said other stereo image isfastened to said second grid device to maintain a fixed relationshipbetween eacH stereo image and the coordinate system provided by the griddevice fastened to that stereo image; and said means for holding twostereo images comprises a first image carrier for holding one stereoimage and a second image carrier for holding the other stereo image. 11.The stereoplotter set forth in claim 10 in which said one stereo imageand first grid device are movably disposed on said first image carrier,and said other stereo image and said second grid device are movablydisposed on said second image carrier to permit an operator to move saidstereo images with respect to said image carriers.
 12. The stereoplotterset forth in claim 8 in which: said viewing means comprise binocularviewing apparatus for viewing said two stereo images simultaneously,said binocular apparatus defining an eye base for the stereoplotter; andsaid means for moving comprises means for moving one of said stereoimages in a direction parallel to said eye base.
 13. The stereoplotterset forth in claim 12 in which: said two stereo images are heldsubstantially in a plane; and said moving means comprises means formoving one of said stereo images in a direction substantiallyperpendicular to said eye base and in said plane.
 14. In a stereoplotterhaving: means for holding two stereo images of a scene; and viewingmeans for providing a first optic path to one of said stereo images anda second optic path to the other stereo image to thereby provide oneviewing the stereo images with a three-dimensional image of said scene,said three-dimensional image comprising a collection of image points,each image point formed from one conjugate point on each of two stereoimages; improved means for providing a floating mark for identifyingpoints of interest in said three-dimensional image comprising: meansdisposed in the first optic path defining a first half mark foridentifying points on the one stereo image shaped to provide both an xcoordinate defining and a y coordinate defining portion of said floatingmark; and means disposed in the second optic path defining a second halfmark for identifying points of interest on the other of said stereoimages shaped to provide only an x coordinate defining portion of saidfloating mark, said two half marks providing a floating mark capable ofidentifying points in said three-dimensional image when said stereoimages are oriented to provide a three-dimensional image having amoderate amount of Y parallax, and when said half marks are placed overconjugate points on the two stereo images.
 15. The stereoplotter setforth in claim 14 further including: means for measuring the x and yimage positions of identified conjugate points on said one stereo image;means for measuring only the x image positions of identified points onsaid other stereo image; and calculating means for using said measuredimage positions to calculate the coordinate position in an undistortedmodel of said scene of points identified in said three-dimensionalimage.
 16. The stereoplotter set forth in claim 15 in which: saidviewing means comprises binocular viewing apparatus for viewing said twostereo images simultaneously, said binocular apparatus defining an xaxis for the stereoplotter parallel to the eye base of said binocularapparatus; and said second half mark comprises a broken straight linesubstantially perpendicular to said x axis, said break defining a ycoordinate position when said second half mark is viewed alone.
 17. Thestereoplotter set forth in claim 15 in which: said means for holdingsaid two stereo images is constructed to hold said images substantiallyin a plane; said viewing means comprise binocular viewing apparatus forviewing said two stereo images simultaneously, said binocular apparatusdefining an eye base for the stereoplotter; and said calculating meanscomprises means for calculating said coorDinate position in saidundistorted model using the formulas: X XL + S''x''16 Y YL + S''y''16 ZZL + S''z''16 where: the X axis of the coordinate system for the abovethree formulas is parallel to said eye base; the Y axis of saidcoordinate system is perpendicular to said X axis and is substantiallyin said plane; the Z axis of said coordinate system is perpendicular tothe X and Y axes; X,Y,Z the coordinates of a point in the scene; XL ,YL,ZL the location in model coordinates of the coordinate origin of theimage coordinate system for one stereo image; S a scale factor relatingimage coordinate scale to model coordinate scale; and x''16, Y''16,z''16 the stereo image coordinates of the one stereo image with itscoordinate origin at XL ,YL ,ZL rotated to be parallel to the modelcoordinate axes.
 18. A stereoplotter for providing coordinate positionsof selected points in an undistorted model of a scene, and indicatingwhether said points lie on a preselected contour in said undistortedmodel comprising: means for holding two stereo images of the scene;viewing means for providing a possibly distorted three-dimensional imageof said scene, said three-dimensional image comprising a collection ofimage points, each image point formed from one conjugate point on eachof said stereo images; means for selecting points of interest in saidthree-dimensional image; means for automatically measuring the imagepositions of conjugate point pairs forming said selected image points insaid three-dimensional image; calculating means for respondingimmediately to said measured image positions and calculating thecoordinate position in an undistorted model of said scene of saidselected image points; and signal means responsive to said calculatedcoordinate positions for providing a signal indicating whether thecalculated elevation of a selected point differs from the elevation of apreselected contour, said signal providing means thereby enabling anoperator to select points along a preselected contour in an undistortedmodel of the scene from a possibly distorted three-dimensional image ofthat scene.
 19. The stereoplotter set forth in claim 18 in which saidsignal providing means provides a first signal to indicate thecalculated elevation of a selected point is higher than said preselectedelevation and a second signal to indicate the calculated elevation of aselected point is lower than said preselected elevation.
 20. Thestereoplotter set forth in claim 18 in which: said viewing meanscomprises a binocular viewing apparatus for viewing said two stereoimages simultaneously, said binocular apparatus defining an x axis forsaid stereoplotter parallel to the eye base of said binocular apparatus;said selecting means comprises means for providing a floating mark forselecting points of interest in the three-dimensional image; and saidsignal providing means comprises means for moving one of said stereoimages along said x axis of said stereoplotter to introduce X parallaxinto said three-dimensional image to raise the elevation of saidfloating mark when said calculated elevation is greater than saidpreselected elevation, and to lower the elevation of said floating markwhen said calculated elevation is lower than said preselected elevation.21. A method for providing an undistorted model of a scene from athree-dimensional image that may be either distorted or undistorted ofthe scene comprising the steps of: providing two stereo images of ascene, said stereo images carrying reference points representingpredetermined locations in the scene; viewing said two stereo imagessimultaneously to obtain a possibly distorted three-dimensional image ofsaid scene, said three-dimensional image comprising a collection ofimage points, each image point formed from one conjugate point on eachof said stereo images; selecting points, lines, and areas of interest insaid three-dimensional image; measuring the image positions of conjugatepoint pairs forming said selected points, lines, and areas of saidthree-dimensional image; using said measured image positions and therelationship between the image positions of said reference points andthe predetermined locations in the scene to calculate the coordinatepositions in an undistorted model of said scene of image points, lines,and areas represented by measured pairs of conjugate points; and forminga representation of the undistorted scene from said calculatedcoordinate positions.
 22. The method set forth in claim 21 in which saidsteps of measuring and calculating said positions are performed byautomatic measuring and calculating apparatus respectively, and in whichsaid step of forming said representation is performed by an automaticgraphing apparatus responsive to said calculated coordinate positions.23. The method set forth in claim 21 further including the step of:recording said measured image positions; and said step of calculatingcoordinate positions in an undistorted model is performed for eachselected conjugate point pair after a record of the image positions ofall selected conjugate point pairs has been provided.
 24. The method setforth in claim 21 in which said step of calculating coordinate positionsin an undistorted model is performed for each selected conjugate pointpair immediately after selection of said point pair to provide a realtime representation of the undistorted model.
 25. The method set forthin claim 21 further including the steps of: recording said measuredimage positions; and inserting control signals into the record of stereoimage coordinates that indicate the classification of recorded pointpairs.
 26. The method set forth in claim 21 in which: said step ofselecting points, lines, and areas of interest includes providing afloating mark to stereoscopically identify and select points, lines andareas of interest in said three-dimensional image; and the methodfurther includes the step of automatically recording the image positionsof conjugate point pairs forming an image point identified by thefloating mark whenever said floating mark is moved a predetermineddistance.
 27. The method set forth in claim 21 in which: said step ofselecting points, lines, and areas of interest includes providing afloating mark to stereoscopically identify and select points, lines, andareas of interest in said three-dimensional image, and moving saidfloating mark along a plurality of parallel lines to select points lyingalong the said lines; and said calculation includes using the imagepositions of said selected points lying along said lines to calculatethe X and Y model coordinate values of points lying along preselectedcontours of said model at preselected intervals.
 28. The method setforth in claim 21 further including the step of forming a trace ofpoints, lines, and areas selected to be of interest, said trace enablingan operator to determine the points, lines, and areas that have beenselected.
 29. The method set forth in claim 28 further including thestep of superimposing an image of said trace onto said three-dimensionalimage.
 30. A method for providing coordinate positions of selectedpoints in an undistorted model of a scene, said points being selectedfrom a three-dimensional image of the scene that may be distorted andthat may be varied during point selection to minimize distortions in onearea of said image comprising the steps of: providing two stereo imagesof the scenE, each stereo image including reference points representingpredetermined locations in the scene; providing a first coordinatemeasuring system for one stereo image and a second coordinate measuringsystem for the other of said stereo images; viewing said two stereoimages simultaneously to obtain a three-dimensional image of said scene,said three-dimensional image comprising a collection of image points,each image point formed from one conjugate point on each of said stereoimages; selecting points defining lines and areas of interest in saidthree-dimensional image; measuring the positions in said coordinatemeasuring systems of conjugate point pairs forming said selected imagepoints; moving one of said stereo images with respect to the other whilemaintaining a fixed spatial relationship between each stereo image andthe coordinate measuring system for said each stereo image, saidrelative movement thereby enabling an operator to vary the stereoquality of and provide stereo fusion in the area of thethree-dimensional image being viewed; and using said measuredcoordinates and the relationship between the positions of said referencepoints in said coordinate measuring systems and in an undistorted modelof the scene to calculate the positions in an undistorted model of saidscene of image points represented by measured pairs of conjugate points.31. The method set forth in claim 30 in which said step of calculatingcoordinate positions in an undistorted model includes: determining therelative positions of said one stereo image in said first measuringcoordinate system and the relative positions of said other stereo imagein said second measuring coordinate system; and converting saidpositions measured in said coordinate measuring systems to stereo imagecoordinate positions; and using said stereo image coordinate positionsto calculate positions in an undistorted model of image pointsrepresented by measured pairs of conjugate points.
 32. The method setforth in claim 31 in which: said step of providing first and secondreference coordinate measuring systems comprises fastening a firstreference grid measuring system to one of said stereo images andfastening a second reference grid measuring system to the other of saidstereo images; and said step of converting coordinate positions in saidcoordinate measuring system to stereo image coordinate positions isaccomplished using the formulas: x xg cos theta + yg sin theta + xo y-xg sin theta + yg cos theta + yo where: x,y stereo image coordinates ofa point xg,yg grid coordinates of the same point xo,yo stereo imagecoordinates of the grid coordinate origin theta angle of rotationbetween the grid and stereo image coordinate systems.
 33. The method setforth in claim 32 in which: said step of measuring positions in saidcoordinate measuring systems comprises measuring the x and y coordinatesof conjugate points on each stereo image; and said calculation of thecoordinate positions in an undistorted model of image points representedby pairs of conjugate image points is performed according to theformulas: X XL + Sx''16 Y YL + Sy''16 Z ZL + Sz''16 where: the X axis ofthe coordinate system for the above three formulas is parallel to theeye base of an observer viewing said three-dimensional image in anordinary manner; the Z axis of said coordinate system is perpendicularto said X axis and defines elevation in said three-dimensional image;the Y axis of said coordinate system is perpendicular to both the X andZ axes; X,Y,Z Model coordinates of a point in the scene; XL ,YL ,ZL thelocation in model coordinates of the coordinate origin of the imagecoordinate system for one stereo image; S a scale factor relating imagecoordinate scale to model coordinate scale; and x''16,y''16,z''16 thestereo image coordinates of the one stereo image with coordinate originat XL ,YL ,ZL rotated to be parallel to the model coordinate axes.
 34. Amethod for providing coordinate positions of selected points in anundistorted model of a scene, said points being selected from athree-dimensional image that may contain a moderate amount of Y parallaxand be otherwise distorted comprising the steps of: providing two stereoimages of the scene; viewing said two stereo images simultaneously toobtain a possibly distorted three-dimensional image of said scene, saidthree-dimensional image comprising a collection of image points, eachimage point formed from one conjugate point on each of said stereoimages; providing a floating mark for selecting and identifying pointsof interest in said three-dimensional image by providing a first halfmark for identifying points on one of said stereo images shaped toprovide both x coordinate defining and y coordinate defining portions ofsaid floating mark, and a second half mark for identifying points ofinterest on the other of said stereo images shaped to provide only an xcoordinate defining portion of said floating mark, said two half marksproviding a floating mark capable of identifying points in saidthree-dimensional image when said stereo images are oriented to providea three-dimensional image having a moderate amount of Y parallax andwhen said half marks are placed over conjugate points on the two stereoimages; selecting points of interest in said three-dimensional imagewith said floating mark; determining the image positions of conjugatepoints forming said selected image points; and using said imagepositions to calculate the coordinate positions in an undistorted modelof said scene of said selected image points.
 35. The method set forth inclaim 34 in which said second half mark comprises a straight linedisposed substantially perpendicular to the eye base of an observerviewing said three-dimensional image in an ordinary manner.
 36. Themethod set forth in claim 35 in which said step of providing said secondhalf mark provides a broken straight line with said break defining a ycoordinate position when said second half mark is viewed alone.
 37. Themethod set forth in claim 34 in which: said step of determining thestereo image coordinates of said conjugate points comprises determiningthe x and y stereo image coordinates of conjugate points on said onestereo image, and determining the x stereo image coordinates ofconjugate points on said other stereo image; and said calculatingcoordinate positions in an undistorted model is performed using theformulas: X XL + S''x''16 Y YL + S''y''16 Z ZL + S''z''16 where: the xaxis of the coordinate system for the above three formulas is parallelto the eye base of an observer viewing said three-dimensional image inan ordinary manner; the Z axis of said coordinate system isperpendicular to said X axis and defines elevations in thethree-dimensional image; the Y axis of said coordinate system isperpendicular to the X and Z axes; X,Y,Z, model coordinates of a pointin the scene; XL ,YL ,ZL the location in model coordinates of thecoordinate origin of the imAge coordinate system for one stereo image;S'' a scale factor relating image coordinate scale to model coordinatescale and the attitude of one stereo image to that of the other;x''16,y''16,z''16 the stereo image coordinates of the one stereo imagewith coordinate origin at XL ,YL ,ZL rotated to be parallel to the modelcoordinate axes.
 38. A method of determining the coordinate positions inan undistorted model of points selected from a possibly distortedthree-dimensional image of a scene, and for indicating whether saidpoints lie on a preselected contour in said undistorted model comprisingthe steps of: providing two stereo images of the scene; viewing said twostereo images simultaneously to obtain a possibly distortedthree-dimensional image of said scene, said three-dimensional imagecomprising a collection of image points, each image point formed fromone conjugate point on each of said stereo images; selecting points ofinterest in said three-dimensional image; determining the stereo imagecoordinates of conjugate point pairs forming said selected image pointsin said three-dimensional image; using said stereo image coordinates tocalculate the coordinate position in an undistorted model of said sceneof an image point immediately after selection of said an image point;and providing a signal indicating the relationship between the elevationof the calculated coordinate position of said an image point and theelevation of a preselected contour.
 39. The method set forth in claim 38in which said step of providing a signal indicating the relationshipbetween said calculated elevation and said preselected elevationcomprises providing a first signal for indicating said calculatedelevation to be greater than said preselected elevation, and providing asecond signal for indicating said calculated elevation to be less thansaid preselected elevation.
 40. The method set forth in claim 38 inwhich: said points of interest in said three-dimensional image areselected with a floating mark formed from a first half mark foridentifying points on one of said stereo images and a second half markfor identifying points on the other of said stereo images; and saidproviding a signal indicating the relationship between the calculatedand preselected elevations comprises providing a relative movementbetween said one stereo image and said one half mark to vary theapparent elevation of said floating mark, said relative movementcomprising movement causing the apparent elevation of said floating markto increase when said calculated elevation is greater than saidpreselected elevation, and to cause the apparent elevation of saidfloating mark to decrease when said calculated elevation is lower thansaid preselected elevation.